I finally have some time to play with the idea of combining Fibaro RGBW-441 module with an Arduino soil moisture sensor to make it work together and I can say that initial results are very promising - it works!
If anyone interested in how-to, below is the receipt:
All you need is a Fibaro RGBW-441 module and 1 up to 4 Arduino compatible soil moisture sensors - I used the one like on this photo: http://img.dxcdn.com/productimages/sku_290154_5.jpg
According to the specification the inputs of RGBW-441 module can be configured and attached to various sensors, giving analog signal within 0-10V range. To do that, you need to define which of inputs (you can configure all, if you want) should act as “Analog” 0-10V input. It is a bit unclear in the manual, so here s the detailed schema: you need to set parameter 14 (2byte dec) with a number reflecting setting for all 4 channels of the module. the number is calculated by converting binary values for each channel to the dec value - you can use online converter.
By default, each channel is set to RGBW - momentary switch, normal mode. The binary sequence for that setting is 0001, so four channels give 0001000100010001 which, converted to decimal system is 4369.
If you want to change i.e. channel 1 to analog input (1000) you have to modify sequence like here 1000000100010001 = 33041. For all four inputs it will be 1000100010001000 = 34952
Remember, that setting specific channel to receive analog input you lose possibility to turn on/off responding output. If you want to have possibility to steer some device (i.e water valve) directly by RGBW-441 module, you can’t use sensor with that channel, at least not directly.
I configured CH 1 and 2 as analog inputs and CH 3 and 4 as “OUT - Toggle with memory (normal mode)”. That gives bin 1000100011101110 = 35054 dec
One thing to remember - if input set to receive 0-10V signal it gives 100% when the circuit is open and 0% if it is closed. Don’t be surprised that after you set specific channel like that, you’ll see 100% (ON) reading when you didn’t attached yet any device to it.
Next thing: Arduino sensor. I’ve decided to try Arduino one because it is cheap (like 2 USD) and available without much effort (OK, you wait for the shipment from China if you want to get best price). The only problem with such sensor is that, according to the specification, it works with power only up to 5V DC.
I tried to find moisture detector with output up to 10V, but all I have found were professional, expensive ones (starting from c.a. 200 USD)
After some tries with powering sensor with 5V and attaching its analog output to RGBW-441 (didn’t work) or considering some step-up/step-down converter to make the sensor working, I finally figured that it may probably work with voltage up to 30V and the information about 5V refers to Arduino compatibility only. I power this setup with 12V, so I decided to give it a try.
And it works!
Attaching the sensor is really simple, you attach + and ground to the same DC power source as RGBW-441 and then analog output (A0) to desired IN channel of RGBW-441 module, and it is done.
Remember, that as I wrote before, Fibaro reports 100% if circuit is open (soil dry) and 0% if it is closed (soil completely wet), so the readings are reversed.
But they seem to be accurate enough to figure out at which level you should set your sprinkles/waterline ON.
If someone have any idea how to reverse these readings, please give a hint.
Another topic is that RGBW-441 is presenting itself as a dimmer, so it goes under “lights on/off” shortcut. I’ve tried to change its category and subcategory to move it out from there, but I didn’t find working combination (some obvious ones, like refrigerator switch, are not accepted by it). Any help here is appreciated as well.